Anytime the UbuntuHashes page is missing a hash, you can check on any of the download servers. Considering that hashes are small and the official, central servers might be less likely to have corrupted or tampered files than others (probably a relatively small risk anyway), I'd suggest using the official, central servers for this.

The most commonly used ISO images for all currently supported releases are available on:

Finally, please note that the MD5SUMS.gpg file is the Ubuntu project's digital signature. Hardly anybody verifies that in this situation (as far as I know), but if you did use GPG to verify it and check the MD5SUMS file against it, then you'd essentially know for sure that they were the correct MD5SUMS. (Of course anyone can create a .gpg file that looks right and signs the file, but it wouldn't check out as being signed with the project's key.)

If you're interested in more information about verifying GPG signatures on checksum files for Ubuntu downloads, I recommend posting a new question.

If I have a corrupt download and it doesn't burn properly, I clearly won't be able to boot off it.
–
Jack M.Oct 25 '10 at 16:43

2

No. I have seem plenty of corrupted CDs that will boot nicely but fail while installing or just while booting some random program. Assuming that the corruption will happen in a place critical to boot is just wrong.
–
Javier RiveraOct 25 '10 at 17:26

The 'releases' subdomain includes all the files associated with a specific release including the md5 hashes. Its also been the home of ubuntu's releases since 2004 so its probably not going away anytime soon.
http://releases.ubuntu.com/precise/